The present invention provides a continuous deaeration system for use in removing air trapped in the high pressure actuating oil rail of a hydraulically-actuated, electronically-controlled, unit injector fuel system, hereinafter referred to as a HEUI fuel injection system. More specifically, the deaeration system comprises an extension tube which seats in the high pressure actuating oil rail which extends longitudinally along on each bank of a V-8 engine. The tube extends into the air pocket at the highest point of the rail adjacent the front injector and causes the air to be purged through the front injector on each bank continuously during engine operation.